1. Field of the Invention
The present invention relates, in general, to winches and hoists, and in particular, to hoists having motorized winches and safety devices therefor.
2. Information Disclosure Statement
This application is a safety improvement that may be used with hoists having motorized winches such as, for example, the hoist disclosed in U.S. Pat. No. 5,105,349 (issued Apr. 14, 1992).
It is often desired to provide a hoist with a motorized winch to raise and lower objects. A typical and well-known hoist is disclosed in U.S. Pat. No. 5,105,349 (issued Apr. 14, 1992) for raising and lowering a chandelier to and from a ceiling in a home or other building, and such a motorized winch typically has a spool or reel on which a hoist cable is wound and unwound to raise and lower an object such as a chandelier.
Two problems are sometimes seen with such winches and hoists. First, sometimes the winch of the hoist is improperly operated when the weighted object (e.g., the chandelier) is not pulling downwardly on the hoist cable. This “unweighted” problem condition may be seen, for example, if a piece of furniture, such as a table, happens to be below the chandelier and an inattentive operator keeps lowering the chandelier until it hits the piece of furniture or even the floor, and, occasionally, a very inattentive operator may keep the winch in a lowering mode past the point when the chandelier hits the piece of furniture or the floor. A similar “unweighted” situation develops if an operator tries to operate the winch when the object's weight is removed, as when the chandelier is removed from the hoist cable. When the winch is operated while in this “unweighted” condition, the hoist cable tends to become tangled and may come off of the winch's spool or reel.
A second problem occurs when an inattentive operator allows the winch to be operated past the point when the hoist cable become fully unwound from the winch spool or reel, such that the winch, still turning in the “unwinding” direction, begins winding the cable back on to the spool or reel in the reverse direction, hoisting the object (e.g., a chandelier) while the winch is still turning in the “unwinding” direction. Some winches have safety cutoff switches that will stop the operation of the winch motor when the hoisted object reaches an upper limit, but some such safety cutoff switches are designed to only operate when the winch is in the “raising” mode, such that the winch spool or reel is turning in the “winding” direction. Because this second problem causes the hoist cable to be improperly wound on the winch spool or reel in the reverse direction, often the safety cut-off switches are ineffective (because the winch is turning in the “unwinding” direction yet the hoist cable is being wound onto the winch spool or reel), and the safety cutoff switch does not stop the operation of the winch when the hoisted object attempts to travel past its upper limit. Such a failure can cause, for example, a chandelier to be hoisted through the ceiling, causing damage, and has been known to cause the hoist cable to break and the chandelier to fall, causing injury and property damage, especially if the winch motor is improperly fused or if the fuse or circuit breaker on the winch has been disabled.
It is therefore desirable to provide a winch safety switch for a hoist such that the winch safety switch disables the operation of the winch motor if the winch is operated in its unwinding/lowering mode when either the hoist cable becomes unweighted or if the winch begins winding the hoist cable in the reverse direction after passing the fully-unwound point.
A preliminary patentability search in class 362, subclasses 147, 384, 404, 391, 418, and 403, for the invention disclosed in U.S. Pat. No. 5,105,349, produced the following patents, some of which may be relevant to the present invention: Farrington et al., U.S. Pat. No. 2,609,170, issued Sep. 2, 1952; Pfaff, U.S. Pat. No. 3,610,584, issued Oct. 5, 1971; Booty et al., U.S. Pat. No. 4,316,238, issued Feb. 16, 1982; and Sakurai, U.S. Pat. No. 4,381,539, issued Apr. 26, 1983. Additionally, during prosecution of the predecessor of the application that issued as U.S. Pat. No. 5,105,349, an advertisement of a floodlight lowering attachment, dated Mar. 11, 1938, manufactured and sold by the Benjamin Company under the name “SAFLOX”, was cited by the Examiner.
Farrington et al., U.S. Pat. No. 2,609,170, describes a motor-driven lamp hanger with multiple embodiments. The Farrington device, as described, has four cables supporting the lamp fixture which are wound on four separate drums. The Farrington patent also describes upper and lower limit switches to shut off the power to the drive motor at the extremes of travel of the lamp fixture, as well as fixed and mating contacts to supply power to the lamp fixture when in the raised position.
Pfaff, U.S. Pat. No. 3,610,584, describes a lowering mechanism for a light fixture which comprises a drive motor and braking mechanism, said drive motor being coupled through a chain drive mechanism to a take-up shaft comprising a pair of drums, each of which winds a flexible ribbon or tape which is attached to the light fixture.
Booty et al., U.S. Pat. No. 4,316,238, describes a light fixture and elevator therefor, comprising a horizontally reciprocal carriage, a biasing spring attached to the carriage, said carriage moving horizontally as the light fixture is raised and lowered. A hydraulic piston may be attached to the carriage of the Booty device for controlling the rate of movement of the carriage, and therefore the descent rate of the light fixture. The Booty device is manually operated and is not motorized, and has no contacts which interrupt the flow of electricity to the light fixture when the light fixture is not in the raised position.
Sakurai, U.S. Pat. No. 4,381,539, describes a manually-operated non-motorized height level adjusting means for a light fixture comprising a string winder with ratchets which winds a plural number of strings or wires, attached to the light fixture, onto a plural number of spools. Also, the Sakurai patent, like the Booty device, has no contacts which interrupt the flow of electricity to the light fixture when the light fixture is not in the raised position.
The advertisement for the Benjamin “SAFLOX” floodlight lowering attachment shows a hand operated non-motorized mechanism that raises and lowers an outdoor floodlight. The mechanism includes two sets of contacts that meet and are protected when the lamp is in the raised position.
None of these references, either singly or in combination, disclose or suggest the present invention.